Method of flattening metal articles



United States Patent 3,501,935 METHOD OF FLATTENING METAL ARTICLES DonP. Clausing, Wilkins Township, Allegheny County, Pa., assignor to UnitedStates Steel Corporation, a corporation of Delaware No Drawing. FiledFeb. 21, 1968, Ser. No. 707,241 Int. Cl. B21d 1/06, 3/00 US. Cl. 72-2078 Claims ABSTRACT OF THE DISCLOSURE A method of flattening bowed metalarticles such as plates, structural shapes, bars, etc. which have aconcave and convex surface. The method involves plastically deformingthe concave surface without exceeding the yield strength of the convexsurface by, for example, rolling the bowed article in contact with asurface having protrusions which cause deformation of the concavesurface.

The present invention relates to a method of flattening metal articlessuch as plates, structural shapes, bars, etc. More particularly, theinvention relates to flattening such articles by applying to theirconcave surface a force sufficient to cause local plastic flow ordeformation of the concave surface without substantially exceeding theyield strength of the convex surface.

Metal articles such as structural plates, bars, etc. have a naturaltendency to bow as a result of normal production processing. The amountof bow in the article may make it unacceptable for commercialapplications. To flatten such bowed metal articles and straighten same,they have been bent to remove the bow, stretched to remove the bow, orrestrained in dies during quenching to prevent bowing. Many devices havebeen employed to perform these methods. However, each of theconventional methods has at least one shortcoming. Firstly, acceptableflatness and straightness cannot always be obtained in some products,particularly those in heat treated form. Secondly, some of theseconventional methods have a strong tendency to break certain types ofproducts, again particularly heat treated products. In most cases,processing is difficult to control and the time and cost of theseflattening operations are often excessive.

The present invention provides a method of flattening and straighteningbowed metal articles by imparting local plastic indentations ordeformation into the concave surface of the bowed article while it is inthe cold condition. Heated articles are much more easily straightenedand flattened but special equipment and processing is necessary. Thepresent invention, however, enables bowed metal articles to be flattenedat room temperatures and in the cold condition.

Plates, structural shapes and bars bow or bend generally because theconcave surface is smaller in area than the convex surface. Localplastic deformation expands the concave surface to coincide with thearea of the convex surface, thereby flattening and straightening thearticle.

The method of flattening and straightening by cold forming throughlocal, plastic deformation in the concave surface possesses a number ofinherent advantages. Thus, for example, with the method in accordancewith the invention there is a very small risk of product breakage, goodcontrol of the flattening and straightening is achieved and all types ofproducts can be flattened and straightened, including heat treatedproducts which cannot be flattened by conventional means.

In accordance with the invention, flattening and straightening byimparting local plastic deformation into the concave surface throughcold forming can be per- "Ice formed in a rolling mill, press or drophammer forge. One means of flattening and straightening in accordancewith a presently preferred embodiment involves the use of a pair offorce applying surfaces, one of which has protrusions thereon. The bowedmetal article to be flattened is compressed between the force applyingsurfaces in such a manner that the surface having protrusions induceslocalized plastic deformation in the concave surface. Sufficient forceis applied to accomplish plastic deformation of the concave surfacewithout substantially exceeding the yield strength of the convexsurface. :In one presently preferred embodiment, the cold forming isaccomplished in a pair of rolls, one of which is smooth and the other ofwhich has protrusions on the roll surface. The bowed article with theconcave urface contacting the roll with protrusions is compressedbetween the rolls causing the concave surface to expand laterally byforming plastic indentations thereon. The lateral expansion of thesurface that was originally concave flattens and straightens the metalarticle. Structural shapes can be flattened and straightened in the sameway with the use of rolls contoured to fit the structural shape.

An alternate means of flattening and straightening with the use of arolling mill involves the use of a die having protrusions as the forceapplying surface. The bowed metal article is cold rolled with theprotrusions in contact with the concave surface of the metal article.Conventional smooth surface rolls may be used in conjunction with one ormore dies, preferably one. In this embodiment, the bowed article issandwiched between a die and a smooth surface roll.

Various patterns of protrusions on the roll or die surface can beusefully employed and any pattern may be used which is capable ofproviding the plastic deformation of the concave surface necessary forflattening.

In another embodiment of the invention, press or drop hammer forges maybe used to flatten bowed metal articles by employing the same principlesas described above in connection with the rolling embodiments. Theconvex surface of the bowed metal article may contact a smooth die orplaten while the concave surface is plastically deformed by a die havingprotrusions on the surface thereof.

In still another embodiment of the invention useful on certain types ofproducts such as bimetallic, dual hardness articles, e.g. plates, whichhave concave and convex surfaces of differing hardness, and wherein theconvex surface is of a greater hardness, such articles may bestraightened by rolling same between plates or rolls having smoothsurfaces. In this embodiment, a separating force is used such that therelatively soft concave surface of the plate is plastically deformed,i.e. its yield strength exceeded, but the yield strength of therelatively hard convex surface of said article is not substantiallyexceeded. In this embodiment, a uniform compressive force is appliedover the entire concave surface wherein as in the previously describedembodiments, plastic indentations, i.e. deformation, of the concavesurface is produced. An obvious advantage of this latter embodiment isthe avoidance of special dies or rolls. However. greater roll force arenecessary.

As discussed above in connection with the earlier described embodiments,flattening and straightening by rolls or dies with protrusions is notlimited to any particular array of protrusions. Different patterns maybe desirable for various situations and desired results. In some cases,for example, flattening in one direction may be desirable and protrusionpatterns for this purpose may comprise a series of linear protrusionsparallel or transverse to the rolling direction producing correspondingdepressions in the article. Plastic deformation by the use ofcheckerboard protrusions will produce equal amounts of flattening inboth directions.

It is apparent from the above that various changes and modifications maybe made without departing from the invention. Accordingly, the scopethereof should be limited only by the appended claims whereby what isclaimed is:

1. A method of flattening by cold forming a bowed metal article such asplate, structural shape, bar or the like, having a concave and a convexsurface which comprises imparting a force to said bowed metal article tocause localized plastic flow of the concave surface withoutsubstantially exceeding the yield strength of the convex surface.

2. A method of flattening a bowed metal article in accordance with claim1 which comprises compressing said bowed article between two forcesapplying surfaces, one of said force applying surfaces being smooth andadapted to contact the convex surface of the bowed article and thesecond of said force applying surfaces having protrusions thereon andbeing adapted to contact the concave surface of said bowed metalarticle, applying sufficient compressive force to said bowed metalarticle with said force applying surface to cause localized plasticdeformation of the concave surface of said article by said protrusionswithout substantially exceeding the yield strength of the convexsurface.

3. A method in accordance with claim 2 wherein said compressive force isapplied by rolling said bowed metal article between a pair of rolls andsaid force applying surfaces are the surfaces of the rolls.

4. A method in accordance with claim 2 wherein said force applyingsurfaces are die surfaces and said com- 4 pressive force is applied byrolling said bowed metal article between said die surfaces.

5. A method in accordance with claim 2 wherein said compressive force isapplied by pressing said bowed metal article in contact with a diesurface having protrusions thereon.

6. A method in accordance with claim 2 wherein said compressive force isapplied by hammering said bowed metal article in contact with a diesurface having protrusions thereon.

7. A method in accordance with claim 1 wherein said bowed metal articlehas a concave and convex surface of different hardnesses with thehardness of the convex surface being greater and said bowed metalarticle is fiattened by rolling same between smooth rolls to plasticallydeform the concave surface without substantially exceeding the yieldstrength of the convex surface.

8. A method in accordance with claim 7 wherein said bowed article is abimetallic dual hardness plate.

References Cited UNITED STATES PATENTS 681,964 9/1901 Hurst 721922,144,783 1/1939 Ungerer 72197 2,771,801 11/ 1956 Wellman 72207 LOWELLA. LARSON, Primary Examiner US. Cl. X.R. 72700, 379, 365

